This invention is directed to a tornado shelter that takes the form of an especially constructed enclosure or room typically provided above-ground, in a house or other building. The enclosure is strong enough to provide a high degree of occupant protection during most tornados and other high wind events.
The Federal Emergency Management Agency (FEMA) has suggested criteria for such above-ground enclosures. The criteria are discussed in the following publications: “National Performance Criteria for Tornado Shelters”, 1st Edition, published May 8, 1999, and “Taking Shelter from the Storm: Building a Safe Room Inside Your House”, Booklet #320, 2nd Edition, published August 1999. According to the criteria the enclosure should be able to withstand wind pressures developed from winds gusting for three seconds at 250 miles per hour. The enclosure must also be able to withstand the impact without perforation of a 15 lb. 2×4 wooden board traveling at a speed of 100 miles per hour horizontally along the board's longitudinal axis and vertically at 67 miles per hour.
A number of inventions related to above-ground tornado shelters have been patented. These are sometimes called safe rooms. Many of these structures form the walls and ceiling of the structure with metal panels. Of particular relevance, U.S. Pat. No. 5,813,174, granted to Waller, taught a shelter that can be easily erected within an existing building from components that can be stacked and shipped in a compact manner. Waller also taught being able to build the enclosure around the installer for ease of installation in a small existing room of a building. Similarly, U.S. Pat. No. 6,415,557, granted to McCalley in 2002, and U.S. Pat. No. 6,415,558, granted to Cherry in 2002, both teach shelters that can be erected within an existing building, from the inside of the enclosure, with components that can be shipped efficiently.
U.S. Pat. No. 6,415,558, granted to Cherry, is particularly concerned with using standard fasteners for connecting the panels of the structure rather than specially made parts. This made manufacturing the enclosure less expensive, and it arguably made the enclosure easier to erect by users without specialized training. Cherry was also particularly concerned with the particular manner in which the entry and exit door was connected to the other components of the enclosure and the operation of the door. On the other hand, McCalley emphasizes that the connections between his panels were designed to allow for “give” or “play” between the panels so as to dissipate the energy imparted from an impact and thereby resist penetration.
U.S. Pat. No. 5,813,174, granted to Waller, teaches connecting the panels of the structure to frame components that are connected to each other and anchored to the ground, while Cherry cites as a benefit of his invention that a “separate, integrated frame structure” is not needed. However, Cherry still teaches and claims connecting his panels at the edges of the enclosure to separate elongated framing members. McCalley, similarly, teaches using separate elongated framing members to connect the panels.